High-density recording medium and recording and/or reproducing device therefor

ABSTRACT

A high-density recording medium including a first surface and a second surface, the second surface being a light incident surface at a normal mounting condition, a clamping area, an information area including a recording layer provided adjacent to the second surface, a transition area extending between the clamping area and the information area, the transition area being defined from an end position of the clamping area to a beginning of the information area, and a slope being formed in the transition area on the first surface. Further, the slope is formed from the end position of the clamping area to a position placed at least a predetermined distance ahead of the start position of the information area, and a gap as a non-slanted area extends between the information area and a closer end of the slope thereto.

This Nonprovisional application is a Continuation Application ofco-pending application Ser. No. 10/859,124, filed on Jun. 3, 2004, whichclaims priority under 35 U.S.C. §119(a) on Patent Application No(s).10-2003-0035523 and 10-2003-0040353 filed in KOREA on Jun. 3, 2008 andJun. 20, 2003, respectively, the entire contents of which are herebyincorporated by reference.

1. TECHNICAL FIELD

The present invention relates to a high-density recording medium, e.g.,an optical disc and a recording and/or reproducing device therefor, andmore particularly to a high-density optical disc that is capable of notcolliding with an objective lens of an optical pickup when thehigh-density optical disc, such as a BD (Blu-ray disc), is improperlyplaced in an optical disc recording and/or reproducing device, e.g.,when the high-density optical disc is placed upside down in the opticaldisc device, and an optical disc recording and/or reproducing device.

2. BACKGROUND ART

As shown in FIG. 1, a general CD (compact disc) is formed with athickness of 1.2 mm and a diameter of 120 mm. Also, the CD has a centerhole of 15 mm in diameter, and a clamping area of 44 mm in diameter,which is formed around the center hole. The clamping area is securelyplaced on a turntable provided in an optical disc device by means of aclamper also provided in the optical disc device.

A data recording layer of the CD, on which data is recorded in a pitpattern, is spaced approximately 1.2 mm from the surface of the CDfacing an objective lens OL of an optical pickup provided in the opticaldisc device. The objective lens OL, which is used in the optical pickupfor the CD, has a relatively small numeral aperture NA. For example, theobjective lens OL has an NA of 0.45.

As shown in FIG. 2, a general DVD (digital versatile disc) is formedwith a thickness of 1.2 mm and a diameter of 120 mm. Also, the DVD has acenter hole of 15 mm in diameter, and a clamping area of 44 mm indiameter, which is formed around the center hole. The clamping area issecurely placed on a turntable provided in an optical disc device bymeans of a clamper also provided in the optical disc device.

A data recording layer of the DVD, on which data is recorded in a pitpattern, is spaced approximately 0.6 mm from the surface of the DVDfacing an objective lens OL of an optical pickup provided in the opticaldisc device. The objective lens OL, which is used in the optical pickupfor the DVD, has a relatively large numeral aperture NA. For example,the objective lens OL has an NA of 0.6.

As shown in FIG. 3, a high-density optical disc, standardization ofwhich has been under discussion recently, such as a BD (Blu-ray disc),is formed with a thickness of 1.2 mm and a diameter of 120 mm. Also, theBD has a center hole of 15 mm in diameter, a clamping area of 33 mm indiameter, which is formed around the center hole and securely placed ona turntable provided in an optical disc device by means of a clamperalso provided in the optical disc device, and a transition area of 42 mmin diameter, which is allocated between the clamping area and aninformation area.

A data recording layer of the BD, on which data is recorded in a pitpattern, is spaced approximately 0.1 mm from the surface of the BDfacing an objective lens OL of an optical pickup provided in the opticaldisc device.

The objective lens of the optical pickup for the BD has the largestnumeral aperture NA. For example, the objective lens has an NA of 0.85.The optical pickup for the BD uses a laser beam having a shortwavelength to reproduce data recorded in a high-density pit pattern orrecord data in a high-density pit pattern, as compared to the opticalpickup for the CD or the DVD.

Specifically, the laser beam having a short wavelength and the objectivelens having a much larger numeral aperture are used in the opticalpickup for the BD. Consequently, a small spot of a laser beam having anincreased amount of light can be focused on the recording layer in astate in which the objective lens of the optical pickup for the BD iscloser to the recording layer of the BD. Furthermore, the lighttransmittance distance of the laser beam having a short wavelength canbe shortened, whereby property change of the laser beam and occurrenceof aberration are minimized.

When a BD 10 is properly placed on a turntable 11 provided in theoptical disc device, as shown in FIG. 4, a general servo operation iscarried out as follows. The BD 10 is rotated at high speed by means of aspindle motor 12, a motor driver 13, and a servo controller 15. Whilethe BD 10 is rotated, the objective lens OL of an optical pickup 14,which is also provided in the optical disc device, focuses on the BD 10based upon a focusing servo operation, by which the objective lens OL ofthe optical pickup 14 is vertically moved within the range of aprescribed working distance WD. After the focusing servo operation iscarried out, data recorded on the disc is normally read or data isnormally recorded on the disc.

When the BD 10 is improperly placed on the turntable 11 of the opticaldisc device, however, for example, when the BD 10 is placed upside downon the turntable 11, as shown in FIG. 5, the recording layer of the BD10 improperly placed on the turntable 11 is, from the objective lens OL,farther by at least 1.0 mm than that of the BD 10 properly placed on theturntable 11.

In this case, the objective lens OL cannot focus on the BD 10 simply bya normal focusing operation for moving the objective lens OL verticallyalthough the BD 10 is rotated at high speed by means of the spindlemotor 12, the motor driver 13, and the servo controller 15.Consequently, the objective lens OL is upwardly moved toward therecording layer of the BD 10 until it moves to the maximum workingdistance WD_Max under the control of the servo controller 15 forcontrolling the focusing servo operation. As a result, the objectivelens OL comes into collision with the BD 10, which may cause the BD 10,the objective lens OL, or an actuator for supporting the objective lensOL to be damaged, or otherwise cause the servo operation to have fatalerrors.

3. DISCLOSURE OF INVENTION

Therefore, the present invention has been made in view of the aboveproblems, and it is an object of the present invention to provide ahigh-density optical disc that is capable of not colliding with anobjective lens of an optical pickup provided in an optical disc devicealthough the objective lens is upwardly moved toward a recording layerof the high-density optical disc until it moves to the maximum workingdistance when the high-density optical disc, such as a BD (Blu-raydisc), is improperly placed in the optical disc device, e.g., when thehigh-density optical disc is placed upside down in the optical discdevice, and an optical disc device therefor.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a high-densityrecording medium, comprising: a clamping area; an information area; anda transition area between the clamping area and the information area,wherein a step from top surface in the transition area to the topsurface in the information area is formed to have a slope down smoothlyto the top surface of the information area.

In accordance with another aspect of the present invention, there isprovided a high-density recording medium, comprising: a clamping area;an information area the thickness of which is smaller than that of theclamping area; and a transition area between the clamping area and theinformation area, wherein a step is formed at the transition area, andwherein a data recording layer is formed at a lower position withrespect to the middle of the disc in the thickness direction of thedisc.

In accordance with another aspect of the present invention, there isprovided an apparatus for recording and/or reproducing data on or from ahigh density recording medium, comprising: an optical pickup for readingor recording data from or on a high-density recording medium; and aservo controller controlling the optical pickup to carry out a servooperation, wherein the optical pickup reads or records data from or on arecording layer of an information area based on the control of the servocontroller, the information area having thickness smaller than that of aclamping area of the high-density recording medium, wherein a transitionarea formed between the clamping area and the information area, a stepformed at the transition area, and the recording layer formed at a lowerposition with respect to half thickness of the recording medium.

In accordance with another aspect of the present invention, there isprovided an apparatus for recording and/or reproducing data on or from ahigh density recording medium, comprising: an optical pickup for readingor recording data from or on a high-density recording medium, whereinthe high-density recording medium having a clamping area, an informationarea, and a transition area between the clamping area and theinformation area, and a step from top surface in the transition area tothe top surface in the information area is formed to have a slope downsmoothly to the top surface of the information area; and a servocontroller controlling the optical pickup to carry out a servo operationto read or record data from or on a recording layer of information area.

In accordance with yet another aspect of the present invention, there isprovided a system for recording or reproducing data on or from ahigh-density recording medium, comprising: a high-density recordingmedium, the recording medium comprising a clamping area, an informationarea, and a transition area between the clamping area and theinformation area, wherein a step from top surface in the transition areato the top surface in the information area is formed to have a slopedown smoothly to the top surface of the information area, and arecording layer located at a lower portion with respect to halfthickness of the information area; and a recording/reproducing devicewhich is able to insert the high-density recording medium, and operableto record or reproduce data on or from the high-density recordingmedium.

4. BRIEF DESCRIPTION OF DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the invention, illustrate the preferred embodiments ofthe invention, and together with the description, serve to explain theprinciples of the present invention.

FIG. 1 is a view showing the disc structure of a general CD (compactdisc);

FIG. 2 is a view showing the disc structure of a general DVD (digitalversatile disc);

FIG. 3 is a view showing the disc structure of a general BD (Blu-raydisc);

FIG. 4 is a view showing the BD properly placed in a general opticaldisc device;

FIG. 5 is a view showing the BD improperly placed in the general opticaldisc device;

FIG. 6 is a cross-sectional view showing a high-density optical discaccording to a preferred embodiment of the present invention;

FIG. 7 is a view showing that the high-density optical disc does notcollide with an objective lens by the provision of a sloping stepaccording to the present invention;

FIG. 8 is a view showing the high-density optical disc according to thepresent invention properly placed in an optical disc device;

FIG. 9 is a view showing the high-density optical disc according to thepresent invention improperly placed in the optical disc device; and

FIGS. 10 to 15 illustrate high-density optical discs according to thepresent invention and results of experiments on the high-density opticaldiscs.

Features, elements, and aspects of the invention that are referenced bythe same numerals in different figures represent the same, equivalent,or similar features, elements, or aspects in accordance with one or moreembodiments.

5. MODES FOR CARRYING OUT THE INVENTION

Now, a high-density optical disc and an optical disc device for readingdata recorded on such a high-density optical disc and recording data onsuch a high-density optical disc according to a preferred embodiment ofthe present invention will be described in detail with reference to theaccompanying drawings.

FIG. 6 is a cross-sectional view showing a high-density optical discaccording to a preferred embodiment of the present invention. As alreadydescribed above with reference to FIG. 3, the high-density optical disc,for example, a BD (Blu-ray disc) 20 is formed with a thickness of 1.2 mmand a diameter of 120 mm. Also, the BD 20 has a center hole of 15 mm indiameter, a clamping area of 33 mm in diameter, which is formed aroundthe center hole and securely placed on a turntable provided in theoptical disc device by means of a damper also provided in the opticaldisc device, and a transition area of 42 mm in diameter, which isallocated between the clamping area and an information area.

A data recording layer of the BD 20, on which data is recorded in a pitpattern, is spaced approximately 0.1 mm from the surface of the BD 20facing an objective lens of an optical pickup provided in the opticaldisc device. The BD 20 is formed such that the thickness of the clampingarea is different from that of the information area. For example, thetransition area of the BD 20 includes a sloping step having a prescribedthickness t of 0.1 to 0.6 mm at the surface of the BD 20 at a longerdistance from the data recording layer of the BD 20, as shown in FIG. 6.Consequently, the thickness of the information area is 0.1 to 0.6 mmsmaller than that of the clamping area.

The step is formed to prevent a collision of the objective lens of theoptical pickup with the BD 20 although the objective lens is upwardlymoved toward the recording layer of the BD 20 to focus on the recordinglayer until it moves to the maximum working distance when the BD 20 isimproperly placed on the turntable of the optical disc device, e.g.,when the BD 20 is placed upside down on the turntable. Specifically, thestep of 0.1 to 0.6 mm in thickness is formed from the end position ofthe clamping area to the starting position of the information area whilehaving a prescribed slope in order to provide a prescribed gap distancebetween the BD 20 and the objective lens, as shown in FIG. 6.

When a BD having a sloping step formed from the end position of theclamping area, which has a diameter of 33 mm, to the starting positionof the information area, which has a diameter of 42 mm, is placed upsidedown in the optical disc device (Example 1), the objective lens OL ofthe optical pickup collides with the BD as the objective lens OL ismaximally moved in the horizontal direction.

In a BD according to a preferred embodiment of the present invention,the sloping step is partially formed on the transition area. Forexample, the sloping step of the BD is formed from the end position ofthe clamping area, which has a diameter of 33 mm, to the position placed2.0 mm ahead of the starting position of the information area, which hasa diameter of 42 mm. Consequently, the objective lens OL of the opticalpickup does not collide with the BD although the objective lens OL ismaximally moved in the horizontal direction when the BD is placed upsidedown in the optical disc device (Example 2).

The sloping step may be formed with a maximum slope length of 3.5 mm(=(40 mm−33 mm)/2) in the radial direction of the disc on the basis ofthe center hole of the optical disc. Also, the sloping step may have aminimum slope length of 1.8 mm (=(40 mm−36.4 mm)/2) in the radialdirection of the disc, considering that the clamping area may beextended above its diameter of 33 mm. It is preferable, however, thatthe sloping step has a minimum slope length of 1.0 mm (=(40 mm−38 mm)/2)in consideration of manufacturing deviation of the optical disc.Consequently, the sloping step preferably has a slope length of 1.0 mmto 3.5 mm in the radial direction of the disc in the embodiment of thepresent invention.

When the BD 20 is properly inserted into the optical disc device asshown in FIG. 8, the clamping area of the BD 20 is safely placed on theturntable 11. In this case, the thickness of the clamping area is notchanged, whereby stable clamping force is maintained. Furthermore, thethickness of the information area is reduced so that a relatively smallcentrifugal force is generated when the BD 20 is rotated at high speed,whereby more stable clamping force is guaranteed.

While the BD 20 is rotated at high speed by means of the spindle motor12, the motor driver 13, and the servo controller 15, the objective lensOL of the optical pickup 14 is vertically moved within the range of aprescribed working distance to carry out a focusing servo operation.After the focusing servo operation is carried out, data recorded on thedisc is normally read, or data is normally recorded on the disc.

Even when the BD 20 is improperly inserted into the optical disc device,for example, the BD 20 is inserted upside down into the optical discdevice as shown in FIG. 9, the clamping area of the BD 20 is safelyplaced on the turntable 11. In this case, however, a gap distance of 0.1to 0.6 mm is formed between the surface of the clamping area placed onthe turntable 11, facing the objective lens OL and the surface of theinformation area facing the objective lens OL by means of the slopingstep formed at the transition area of the BD 20.

Consequently, the objective lens OL of the optical pickup 14 does notcollide with the BD 20 although the objective lens OL of the opticalpickup 14 is maximally moved in the vertical direction to carry out afocusing servo operation while the BD 20 is rotated at high speed bymeans of the spindle motor 12, the motor driver 13, and the servocontroller 15. Furthermore, the data recording layer of the BD 20 isspaced apart from the surface of the BD 20 facing the objective lens OL,whereby no normal focusing operation is carried out, and thus it isrecognized that no disc is in the optical disc device.

Moreover, the maximum working distance of the objective lens OL isfurther increased, which is advantageous to carry out the focusing servooperation. The thickness of the information area of the BD 20 is reducedbelow 1.2 mm, whereby the cost of materials required to manufacture theBD 20 is decreased. In the case that the BD 20 is manually inserted intoa slot-type optical disc drive, the BD 20 may collide with the opticaldisc drive due to the step formed at the BD 20. However, a shock due tothe collision of the BD 20 with the optical disc drive is minimized bymeans of the sloping shape of the step, whereby smooth insertion of theBD 20 into the optical disc drive is possible.

The reason why the sloping step having a thickness of 0.1 mm to 0.6 mmis formed at the transition area of the BD will now be described. Asshown in FIG. 10, the maximum thickness of the clamping area of the BDis 1.3 mm. Consequently, the thickness of an injection-molded substrateis 1.2 mm with the exception of a cover layer of 0.1 mm in thickness.

When the step is formed on the surface of the BD opposite to the coverlayer so that the information area and the rim area are manufacturedwhile the thickness of the information and rim area is smaller than thatof the clamping area, for example, the thickness of the injection-moldedsubstrate at the information area and the rim area is 0.6 mm, which isthe same as a general DVD, a transcription property of grooves or pitsformed at the recording surface during the injection molding is notdeteriorated as in the DVD.

Consequently, when the thickness of the clamping area is 1.2 mm as shownin FIG. 10, the substrate at the information area and the rim area canbe easily manufactured without deterioration of injection-molding andtranscription properties as long as the thickness of the substrate atthe information area and the rim area is 0.6 mm. As a result, the stephaving a thickness of up to 0.6 mm can be formed between the clampingarea and the information area.

When the cover layer of 0.1 mm in thickness is formed on the recordingsurface of the BD, it is possible to manufacture a BD having a clampingarea whose thickness is 1.3 mm, an information area whose thickness is0.7 mm, and a rim area whose thickness is 0.7 mm. When the minimumthickness of the clamping area is 1.15 mm, and the thickness of the stepis 0.6 mm, the thickness of the information area and the rim area is0.55 mm. Consequently, the thickness of the injection-molded substrateis 0.45 with the exception of the thickness of the cover layer, which is0.1 mm. In this case, however, the injection-molded substrate having athickness of 0.45 mm can be practically manufactured.

On the other hand, the reason why the minimum thickness of the step isset to 0.1 mm is as follows. Even when the objective lens for the BDhaving a numeral aperture of 0.85 has a large working distance, forexample, approximately 0.5 mm or more, as shown in FIG. 11, a collisionof the objective lens with the BD is prevented by the provision of thestep having a thickness of at least 0.1 mm. Specifically, a collision ofthe objective lens with the BD is effectively prevented even when thedistance in which the objective lens can be vertically moved to carryout the focusing servo operation is 0.5 mm in the direction close to therecording surface of the disc and 0.5 mm in the direction away from therecording surface of the disc on the basis of the focusing position.When the working distance of the objective lens is large, the effect ofprevention of the collision of the objective lens with the BD isincreased as the step of the BD has a larger thickness. When the workingdistance of the objective lens is small, however, the collision of theobjective lens with the BD can still be prevented although the step ofthe BD has a small thickness.

When the injection-molded substrate having a thickness of 1.1 mm/0.8 mmand the cover layer having a thickness of 100 μm are manufactured withpolycarbonate, as shown in FIG. 12, so that the thickness of theclamping area is 1.2 mm, and the thickness of the information area andthe rim area is 0.9 mm, the radial angular deviation α has the maximumvalue (α=0.70 degree), which is required under normal test conditionsapplied to the BD, i.e., a temperature of 23±2° C., a relative humidityof 45% to 55%, and an atmospheric pressure of 86 kPa to 106 kPa.

When the injection-molded substrate is made of polycarbonate as shown inFIG. 13, the angular deviation (α=0.80 degree) is satisfied under thesudden change test conditions of the BD, i.e., a condition in which therelative humidity is changed from 95% to 45%, and the temperature is 25°C., which is unchanged, and another condition in which the relativehumidity is changed from 45% to 30.0%, and the temperature is changedfrom 25° C. to 70° C. while a prescribed level of the absolute humidityis maintained, as long as the thickness of the disc, i.e., the thicknessof the disc in information area is at least 0.9 mm. However, it isdifficult to satisfy the above-mentioned conditions when the thicknessof the disc is below 0.9 mm. Consequently, it is preferable to set theminimum thickness of the disc to 0.9 mm when the injection-moldedsubstrate is made of polycarbonate. However, it is possible tomanufacture a disc having a thickness of below 0.9 mm when theinjection-molded substrate is made of one of other plastic materialshaving higher strength than that of the polycarbonate.

When the disc is directly loaded into or unloaded from a slot-type discdrive, which has no tray, as shown in FIG. 14, the disc may be caught bythe disc drive due to the vertical step formed at the disc, which leadsto a failure to load the disc into the disc drive. When the disc ismanufactured such that the sloping angle of the step is not more than 30degrees (=0.6 mm/1.0 mm) as shown in FIG. 15, however, the disc is notcaught by the disc drive due to the slope provided at the step.

Although the preferred embodiments of the present invention have beendisclosed for illustrative purposes, those skilled in the art willappreciate that various modifications, additions and substitutions arepossible, without departing from the scope and spirit of the inventionas disclosed in the accompanying claims. For example, the step formed atthe transition area of the disc may have other shapes in addition to theaforesaid sloping shape.

As apparent from the above description, the present invention provides ahigh-density optical disc wherein a prescribed gap distance between thehigh-density optical disc and an objective lens of an optical pickupprovided in an optical disc device is increased. Consequently, thepresent invention has an effect of preventing a collision of thehigh-density optical disc with the objective lens of the optical pickup,whereby damage to the high-density optical disc or the objective lens ofthe optical pickup is prevented, and fatal errors of a servo operationare effectively prevented.

1. A high-density recording medium, comprising; a first surface and asecond surface, the second surface being a light incident surface at anormal mounting condition; a clamping area; an information areaincluding a recording layer provided adjacent to the second surface; atransition area extending between the clamping area and the informationarea, the transition area being defined from an end position of theclamping area to a beginning of the information area; and a slope beingformed in the transition area on the first surface, wherein the slope isformed from the end position of the clamping area to a position placedat least a predetermined distance ahead of the start position of theinformation area, and wherein a gap as a non-slanted area extendsbetween the information area and a closer end of the slope thereto. 2.The recording medium as set forth in claim 1, wherein the predetermineddistance is 2.0 mm.
 3. The recording medium as set forth in claim 1,wherein the high-density recording medium is a Blue-ray Disc™.
 4. Therecording medium as set forth in claim 1, wherein the recording layer islocated at a distance of about 0.1 mm from the second surface.
 5. Therecording medium as set forth in claim 1, wherein the transition areaextends between 33 mm diameter and 42 mm diameter of the recordingmedium.
 6. The recording medium as set forth in claim 1, wherein theslope has a thickness 0.1 mm<t<0.6 mm.
 7. The recording medium as setforth in claim 1, wherein the slope has a thickness so as not to collidewith an objective lens of an optical pickup to focus on the recordinglayer.
 8. The recording medium as set forth in claim 1, wherein theslope has a maximum slope length of 3.5 mm.
 9. The recording medium asset forth in claim 1, wherein the slope has a minimum slope length of1.8 mm.
 10. The recording medium as set forth in claim 1, wherein theslope ends at 40 mm diameter of the recording medium.
 11. The recordingmedium as set forth in claim 1, wherein the clamping area has athickness of maximum 1.3 mm.
 12. The recording medium as set forth inclaim 1, wherein the information area has a thickness of minimum 0.9 mm.13. The recording medium of claim 1, wherein the second surface coveringthe clamping area, the transition area and the information area issubstantially coplanar.
 14. An apparatus for recording data on a highdensity recording medium, comprising: an optical pickup configured torecord data on the recording medium, the recording medium having a firstsurface and a second surface, the second surface being a light incidentsurface at a normal mounting condition, a clamping area, an informationarea having a recording layer provided adjacent to the second surface, atransition area extending between the clamping area and the informationarea and being defined from an end position of the clamping area to abeginning of the information area, and slope being formed in thetransition area on the first surface; and a servo controller configuredto control the optical pickup to carry out a servo operation to recorddata on the recording medium, wherein the slope is formed from the endposition of the clamping area to a position placed at least apredetermined distance ahead of a start position of the informationarea, and wherein a gap as a non-slanted area extends between theinformation area and a closer end of the slope thereto.
 15. Theapparatus of claim 14, further comprising: a clamping unit configured toclamp the clamping area of the recording medium by a predeterminedforce.
 16. The apparatus of claim 14, wherein the optical pickupincludes an objective lens, and the objective lens has a workingdistance in a vertical direction to focus the recording layer by thecontrol of the servo controller.
 17. The apparatus of claim 16, whereinthe servo controller is further configured to control the objective lensto move in vertical direction up to maximum working distance to focusthe recording layer when the recording medium is placed upside down on aturntable.
 18. The apparatus of claim 17, wherein the servo controlleris further configured not to focus the recording layer even if theobjective lens is moved to the maximum working distance when therecording medium is placed upside down on a turntable.
 19. The apparatusof claim 18, wherein the servo controller is further configured not togenerate a signal for indicating a focus error, thereby determining thatno recording medium is inserted in the apparatus.
 20. An apparatus forreproducing data from a high density recording medium, comprising: anoptical pickup configured to read data from the recording medium, therecording medium having a first surface and a second surface, the secondsurface being a light incident surface at a normal mounting condition, aclamping area, an information area having a recording layer providedadjacent to the second surface, a transition area extending between theclamping area and the information area and being defined from an endposition of the clamping area to a beginning of the information area,and slope being formed in the transition area on the first surface; anda servo controller configured to control the optical pickup to carry outa servo operation to read data from the recording medium, wherein theslope is formed from the end position of the clamping area to a positionplaced at least a predetermined distance ahead of a start position ofthe information area, and wherein a gap as a non-slanted area extendsbetween the information area and a closer end of the slope thereto. 21.The apparatus of claim 20, further comprising: a clamping unitconfigured to clamp the clamping area of the recording medium by apredetermined force.
 22. The apparatus of claim 20, wherein the opticalpickup includes an objective lens, and the objective lens has a workingdistance in vertical direction to focus the recording layer by thecontrol of the servo controller.
 23. The apparatus of claim 22, whereinthe servo controller is further configured to control the objective lensto move in vertical direction up to maximum working distance to focusthe recording layer when the recording medium is placed upside down on aturntable.
 24. The apparatus of claim 23, wherein the servo controlleris further configured not to focus the recording layer even if theobjective lens is moved to the maximum working distance when therecording medium is placed upside down on a turntable.
 25. The apparatusof claim 24, wherein the servo controller is further configured togenerate a signal for indicating a focus error, thereby determining thatno recording medium is inserted in the apparatus.